CAIRO — Islamist supporters of ousted president Mohamed Morsi clashed with Egyptian security forces and fought brutal street battles with Morsi opponents deep into early hours of Saturday morning, as violence surged following Wednesday’s military coup.

The violence left at least 30 people dead, and more than 1,000 injured across the country, according to Egypt’s health ministry.

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Military rule in Egypt

Frustrated, angry civilians divided themselves into warring camps that went after each other with clubs, rocks and gasoline bombs over a major bridge and thoroughfares in central Cairo, in scenes that recalled the revolution that ousted autocrat Hosni Mubarak in 2011.

So chaotic and fast-moving were events that Egyptian television news broadcasters split their screens into not just two but often three competing scenes of violent unrest.

Near midnight, government troops in armored personnel carriers roared up to protect state media offices from advancing crowds of Morsi supporters. Many of them were drawn from the ranks of the Muslim Brotherhood, which suddenly finds itself shoved out of power and into a more familiar role as an oppressed opposition group.

The day’s turbulent developments reflect an ominously divided country, and region. From beyond Egypt, radical Web sites called for jihad against the nation’s military, even as most Arab governments continued to look on approvingly of the coup. The United States has expressed concern but has generally avoided taking sides.

The president’s ouster “divided this country in two,” said Ali Mohamed Serag, a bureaucrat at Egypt’s Ministry of Electricity. He said he did not belong to the Brotherhood but was distraught by the military’s action: “If people are mad at Obama, they don’t kick him out in a coup.”

Islamist activists chanted that they would see their legitimate president restored to power or die as martyrs. They vowed not to leave their encampment around the Rabia al-Adawiya mosque until the democratically elected head of state is restored.

Addressing tens of thousands of supporters outside the mosque Friday evening, Mohammed Badie, the supreme guide of the Muslim Brotherhood, called for an end to “the military coup” and demanded that the armed forces return Morsi to power.

“All of these millions will stay in the fields, in the squares, until we carry our elected president, President Mohamed Morsi, on our shoulders,” he told the cheering crowd. “Our peacefulness is stronger than your bullets, stronger than tanks and armored vehicles.”

Another speaker called Morsi’s forced removal an assault on the dignity of the people of Egypt. “There are Americans and Zionists behind this,” said the cleric, Salah Sultan.

A mile away, a tense standoff developed outside the gates of the Republican Guard officers club, where Morsi supporters think the former president is being held under house arrest alongside a dozen close aides. According to pro-Morsi eyewitnesses, Egyptian security forces opened fire with birdshot and launched tear gas at Morsi supporters demonstrating outside the gates.

At least one young man was killed by a shot to the head, the moment recorded in a widely circulated and gruesome video clip.

Tahrir Square, meanwhile, began to fill with Egyptians who supported Morsi’s removal and who had heeded calls to defend the renowned protest arena from Morsi’s backers.

Morsi and dozens of his Muslim Brotherhood loyalists were detained Wednesday night and Thursday even as Egypt’s newly named interim president promised to include the Brotherhood in a national unity government. Morsi and his top aides were placed under house arrest, and at least three other Brotherhood officials were taken into custody.

The group’s strongman and deputy chief, Khairat el-Shater, was arrested Friday, according to the Interior Ministry. Islamist leader Hazem Salah Abu Ismail and his brother were also reported to have been arrested, on charges of instigating the killing of anti-Morsi protesters. Abu Ismail has a large following among Salafists, and his arrest could mobilize angry followers of the puritanical Islamist movement, analysts said.

The interim president, Adly Mansour, a little-known judge from the constitutional court, further consolidated his power Friday by dissolving Egypt’s Islamist-dominated upper house of parliament, state television reported. The Shura Council had taken up legislative powers after a court order dissolved the lower house last year.

On Friday, the African Union suspended Egypt’s membership, saying the ouster of Morsi — Egypt’s first democratically elected president — falls under the organization’s doctrine on unconstitutional government changes.

The U.S. State Department condemned Friday’s violence and urged the Egyptian people to “come together to resolve their differences peacefully, without recourse to violence or the use of force.”

Judging by the mood on the streets, there seemed little prospect of that.

“We will have our legitimate president, or we will die as martyrs,” said Mohamed Abu el-Makatem, an agronomist who traveled from Alexandria to the Rabia al-Adawiya Mosque to attend the demonstrations. Some of the men wept as they prayed. Military helicopters circled the area, and jets streaked overhead.

Many in the pro-Morsi crowd waved the red, white and black Egyptian flag, just as thousands of anti-Morsi protesters had done Wednesday before the military forced the president from power. To the right of the stage, the black flag with white lettering used by the extremist group al-Qaeda and its affiliate Jabhat al-Nusra, which is fighting alongside Syrian rebels against President Bashar al-Assad, was clearly visible.

The potential for violence became apparent early Friday when suspected Islamist militants attacked security forces in at least four sites in the tumultuous northern Sinai Peninsula region, according to local news reports that cited security officials.

One security official was killed and three were injured in a rocket attack on a police checkpoint near the Rafah border crossing into the Gaza Strip. Other attacks were reported on a police station and the el-Arish airport. Egyptian security forces promptly sealed the border with Gaza until further notice.

Radical Islamists, inside and outside of Egypt, have called for violence to reverse the military coup. A posting on a jihadist Web site Friday announced the creation of a group, Ansar al-Sharia in Egypt, or Partisans for Sharia in Egypt, with the stated goal of arming and training Egyptian Muslims to wage war against the new government.

“We offer our blood in the place of Muslims and their honor,” stated the Web posting, a translation of which was provided by Site Intelligence Group, a nonprofit organization that monitors jihadist Web sites. The group rejected democracy as anti-Islamic and called on Egyptian Muslims to “truly rise against everyone who stands in the path of implementation of the Sharia,” or Islamic law. It singled out Egypt’s Christian minority for responsibility for the coup.

Two of al-Qaeda’s largest affiliates in the region also called for violence to overthrow the military-installed government. The Somalia-based al-Shabab declared in a statement that “change comes by the bullet alone, not the ballot.” And a Web posting by al-Qaeda in the Islamic Maghreb called the Egyptian coup a “cancer” inflicted by the United States and Israel. It said Egyptians should insist on ridding the country of everything non-Muslim.

Amro Hassan, Abigail Hauslohner and Sharaf al-Hourani in Cairo and William Branigin, Joby Warrick and Debbi Wilgoren in Washington contributed to this report.

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